Method and apparatus for measuring an entity of a magnetic field by using a hall plate, an excitation signal and a detection signal

ABSTRACT

Method and apparatus for measuring an entity of a magnetic field using a Hall sensor which is provided with at least one Hall plate which has a group of two pairs of terminals located at a distance from one another, an excitation signal supplied from a source to one pair of terminals and a detection signal, which forms a representation of the entity, which is tapped off from the other pair of terminals by a processing circuit. The source is a voltage source of which an impedance is negligible for use of the sensor, and the processing circuit has a negligible input impedance for tapping off me detection signal as a short-circuit current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/NL2004/000573, filed Aug. 13, 2004, which claims the benefit ofNetherlands Application No. NL 1024114, filed Aug. 15, 2003, thecontents of which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a method and apparatus for measuring a magneticfield by using a Hall sensor.

BACKGROUND OF THE INVENTION

Sensors which make use of the well-known Hall effect have long been inwidespread use, in particular for carrying out measurements on magneticfields. In addition to the basic application of measuring the magneticfield strength, these sensors—referred to below as “Hall sensors”—arealso used, for example, to measure the position, direction androtational speed. A conceivable example of the latter application is themeasurement of the rotational speed of gearwheels and driveshafts inmachines. In addition, the Hall sensor serves, for example, to measurethe change in the magnetic field strength when machine componentsconsisting of a magnetic material, such as for example the teeth of asteel gearwheel, pass through the magnetic field of a permanent magnet.In this respect, it is also well known for the Hall sensors to be usedin anti-lock brake systems (ABS) for vehicles. For many applications, itis essential for the permanent magnets/magnetic parts used to be assmall and lightweight as possible. However, one significant drawback inthis respect is the fact that Hall sensors according to the currentstate of the art are relatively unsuitable for the accurate measurementof weak magnetic fields (with a magnetic field strength of less than onemilli-Tesla). This drawback generally has the effect of increasingcosts. For example, for Hall sensors to be used effectively in theabovementioned ABS systems, it is necessary to use expensive rare earthmagnets in order to create a sufficiently high magnetic field strengthto allow sufficiently accurate measurements to be carried out with theaid of the sensor. Also, applications of this nature impose high demandson the linearity and accuracy of the required electronic amplificationand signal-processing features and on the sensor housing, which likewisehas the effect of increasing costs.

For many applications, it is desirable for Hall plates, generallytogether with amplification and signal-processing electronics, to beintegrated in semiconductor material, for example in silicon using thewell-known CMOS process. In addition to the advantage of simpleintegration of electronic components in silicon, this also has thedisadvantage that the measurement accuracy and sensitivity of Hallplates according to the current state of the art are in fact adverselyaffected by factors which are inherent to their integration in siliconsemiconductor material.

The traditional principle of carrying out measurements on magneticfields using Hall plates, when using Hall plates integrated in siliconsemiconductor material, also has an adverse effect on the measurementaccuracy and sensitivity of the sensor. This is because in thistraditional measurement principle, a current is used as excitationsignal, and the resulting Hall voltage is measured, forming arepresentation of the field strength of the magnetic field in which thesensor is situated. One significant drawback of this is thatmathematical analysis is able to demonstrate that an integrated Hallsensor has non-linearities which are dependent on an electric voltageand are very difficult to compensate for when using the abovementionedprinciple of current excitation and voltage detection.

The most important factors inherent in their integration in siliconsemiconductor material which have an adverse effect on the measurementaccuracy and sensitivity of Hall plates integrated in siliconsemiconductor material in accordance with the current state of the artare:

-   -   offset voltages caused by mechanical stresses in the crystal        lattices of the semiconductor materials used via the        piezo-resistance effect;    -   offset voltages caused by the Seebeck effect: temperature        differences create a position-dependent contact potential at the        transition between semiconductor material and metal terminals at        different locations on the Hall plate;    -   offset voltages caused by local geometric inaccuracies in the        semiconductor material, formed during the integration process        (for example alignment errors for the terminals, etching        variations);    -   offset voltages resulting from accumulated charge at the        transition between silicon and silicon oxide;    -   offset and non-linearities of electronic features for, for        example, amplifying and processing output signals from Hall        plates, the said circuits likewise being adversely affected by        the abovementioned factors if they are integrated in        semiconductor material, whether or not on the same substrate as        the associated Hall plates themselves.

Offset voltages in Hall sensors may be greater by a factor of 1000 thanthe Hall voltages which are ultimately to be measured. In the past,therefore, various methods have been developed attempting to compensatefor the various offset voltages and other disadvantageous factors inorder to increase the measurement accuracy and sensitivity of Hallsensors.

In a first approximation, a Hall plate can be modelled as a balancedresistance bridge (Wheatstone bridge). The abovementioned stresses inthe crystal lattice of the semiconductor materials used changes thelevel of certain resistances in the bridge, resulting in the formationof an offset voltage which may be of the order of magnitude of a fewtens of milli-Tesla. In addition, the abovementioned Seebeck effect isresponsible for a static (current- and voltage-independent) offsetvoltage of the order of magnitude of a few milli-Tesla. This offsetvoltage is added to the output (Hall) voltage of the Hall plate. TheHall plate then delivers an output voltage where no magnetic field ispresent. The magnetic field strength which would have to be measuredwith an “ideal” Hall plate in order to generate a Hall voltage of thesame order of magnitude as this offset voltage may easily amount toseveral tens of milli-Tesla.

By mathematical analysis, it is possible to demonstrate that theabovementioned static offset resulting from the Seebeck effect can becompensated by carrying out measurements in pairs, with the direction ofthe excitation current being reversed for the second sub-measurement ineach case and the difference in the Hall voltage resulting from the twosub-measurements then being determined.

Mathematical analysis can also be used to demonstrate that theabovementioned offset resulting from stresses can be compensated for bycarrying out measurements using two Hall plates, with the second Hallplate rotated through 90° with respect to the first. The difference inthe output (Hall) voltages from the two Hall plates is in each casedetermined. U.S. Pat. No. 5,241,270 uses this method in modified form,with two Hall plates employed simultaneously, so that the twomeasurements mentioned above can be carried out simultaneously, ratherthan in succession.

Numerous known methods which attempt to compensate for the offsetresulting from stresses are based on a configuration also known as an“orthogonally switched Hall plate”, since the current directions of theexcitation currents are perpendicular to one another in the twosub-measurements. Most Hall sensors according to the current state ofthe art comprise a square Hall plate with electrical terminals at thecorners. In the case of the abovementioned offset compensation methodusing orthogonally switched Hall plates, the measurements are in mostcases carried out in pairs, in which case in the first sub-measurementan excitation current is passed through the Hall plate between twoopposite terminals, and the resulting Hall voltage is measured acrossthe two other, opposite terminals. Instead of reversing the direction ofthe excitation current as described above, for the secondsub-measurement the pairs of terminals for the excitation current andthe Hall voltage are swapped over, so that the direction of theexcitation current is now rotated through 90° with respect to thedirection in the first sub-measurement. The polarity of the Hall voltagewhich is measured during the second sub-measurement is then inverted,and this voltage is added to the measured Hall voltage from the firstsub-measurement. Inter alia, patent documents U.S. Pat. No. 5,406,202,U.S. Pat. No. 5,844,427, EP 1 010 987 A2 and EP 1 130 360 A2 describeHall sensors in which offset compensation methods of this type withorthogonally switched Hall plates are used. This method can only providecomplete offset compensation if the Hall plates used were to have acompletely linear behaviour in functional respects. On account of theirdesign, however, Hall plates formed in semiconductor material areinherently nonlinear. It can be demonstrated that the most importantnonlinearities in Hall plates are dependent on an electric voltage.However, since the offset compensation methods described above usecurrent excitation and voltage detection, it is impossible to completelycompensate for nonlinear offset terms. Moreover, according to the methoddescribed of orthogonal switching of Hall plates, the direction of theexcitation current cannot be completely (180°) reversed, but rather canonly be turned through 90°, and consequently the offset resulting fromthe Seebeck effect is not compensated for, with the result that asignificant offset term remains present. The literature has disclosedoffset compensation methods which make use of the abovementionedorthogonal switching, but through 360° rather than through 90°. Hallsensors in which this method is used are known in the literature asspinning current Hall sensors. The Hall plates used in this case aregenerally provided with eight terminals and have a symmetry which issuch that in each case a straight connecting line between two oppositeterminals is orthogonal (perpendicular) with respect to a straightconnecting line between two other terminals. In this case, during eightsub-measurements, in each case a fixed excitation current passes betweentwo opposite terminals, and the associated Hall voltage is measuredbetween the two terminals whose straight connecting line is orthogonalwith respect to the straight connecting line between the two terminalsmentioned first. The resulting Hall sensor is produced by the GermanFraunhofer IIS. The relatively large number of terminals of the Hallplate in this sensor, however, is responsible for an undesirablereduction in the sensitivity of the sensor with respect to Hall plateshaving a smaller number of terminals. In this case too, currentexcitation and voltage detection are used, and consequently nonlinearoffset terms are not fully compensated for.

U.S. Pat. No. 5,621,319 describes a method for compensating for theoffset resulting from mechanical crystal stresses in integrated Hallsensors. Use is made of the above-described spinning method withorthogonal switching of the Hall plate. In addition, use is made ofvoltage excitation rather than current excitation. However, the drawbackis that this voltage excitation is combined with voltage detection, andconsequently the offset resulting from stresses is not in factcompensated for, on account of the directional-dependent nature ofelectrical properties of the semiconductor material (anisotropy).

In many patent documents, such as the abovementioned U.S. Pat. No.5,406,202 and U.S. Pat. No. 5,844,427, which describe methods forcompensating for the offset resulting from crystal stresses inintegrated Hall sensors, it is attempted to achieve initial offsetcompensation by parallel-connection of a plurality of Hall plates whichare rotated through a defined angle with respect to one another. In mostcases, this involves two Hall plates which are rotated through an angleof 90° with respect to one another. It can be demonstrated bymathematical means that this approach can only function optimally iffour Hall plates are connected in parallel, of which the second, thirdand fourth plates are respectively rotated through 90, 180 and 270° withrespect to the first plate, and if voltage excitation and currentdetection are also used. Document EP 1 206 707 B1 does indeed use aconfiguration with four Hall plates, but these plates are only rotatedthrough in each case 45° rather than 90°. In functional terms, the fourHall plates in this case in reality form a single spinning current Hallplate with eight terminals, as described above, with the associateddrawbacks as likewise described above.

A further significant source of offset in Hall sensors is the offset andnonlinearity of electronic features for, for example, amplifying andprocessing output signals from Hall plates. The fact that theseelectronic features are often integrated with the Hall plates in thesame semiconductor substrate offers possibilities for, for example,combining compensation for the offset of an integrated amplifier withcompensation for the offset of a Hall plate resulting from the Seebeckeffect. U.S. Pat. No. 6,154,027 describes a method in which the outputsignal of a spinning current Hall plate is firstly pre-amplified beforebeing demodulated. However, this involves spinning through 90° in twostages rather than spinning through 360° in four stages. Consequently,the offset resulting from the SEEBECK effect is not compensated for.

The offset resulting from mechanical crystal stresses in thesemiconductor material of a Hall sensor varies for different crystaldirections. Nevertheless, the relevant literature in this field providesscarcely any information about the optimum orientation of a Hall platein semiconductor material. Research carried out by the Applicant hasdemonstrated that the sensitivity of a Hall plate to stress can bereduced by a factor of 10 by selecting the appropriate orientation.

To summarize, on the basis of what has been stated above, it can beconcluded that hitherto it has not been possible to solve the problemsinherent to the current state of the art in this field in order tosufficiently compensate for the effect of factors which have a negativeinfluence on the measurement accuracy and sensitivity of integrated Hallsensors.

It is an object of the present invention to eliminate the abovementioneddrawbacks.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved by the provision ofa method as described below.

One significant advantage obtained as a result is that for each Hallplate used, there are no nonlinearities dependent on an electricvoltage. Even for the above-described method for initial compensationfor the offset resulting from crystal stresses in integrated Hallsensors by parallel connection of a plurality of Hall plates rotatedwith respect to one another to function optimally, it is moreadvantageous to use the voltage excitation/current detectioncombination.

Furthermore, according to the method of the invention, to performmeasurements on magnetic fields using a Hall sensor, it isadvantageously possible to use Hall plates whose largest plane has twopairs of terminals (A1, A2) and (B1, B2), with the terminals of eachpair of terminals being placed at opposite positions in the said planeof the plate, and with the abovementioned plane of the plate beingshaped in such a manner that the abovementioned plane of the plate ismirror-symmetrical with respect to the straight connecting line betweenthe two terminals of a pair of terminals. Measurements using Hall platesaccording to the invention of this type are then characterized by thefact that an excitation voltage V_(ex)(X+, Y−) is applied to a pair ofterminals (X, Y), with (X, Y)∈{(A1, A2), (B1, B2)}, and the detectioncurrent I_(det)(X→Y) which flows through the Hall plate between theterminals of the other pair of terminals being measured withshort-circuited terminals of the latter pair of terminals, themeasurement being carried out in four stages

{V_(ex)(A1, A2), I_(det)(B1→B2)}

{V_(ex)(B1, B2), I_(det)(A2→A1)}

{V_(ex)(A2, A1), I_(det)(B2→B1)}

{V_(ex)(B2, B1), I_(det)(A1→A2)}

which can be run through in any desired order, during which period thetype and signal form of the excitation voltage remain constant, afterwhich a representation of the measured variable is determined viaelectronic processing from the four measured values for the detectionsignal I_(det)(X→Y). However, the nature and/or signal form of theexcitation voltage can be altered between the abovementionedmeasurements comprising four stages. In many cases, the abovementioned“measured variable” will be the magnetic field strength.

This is therefore a spinning voltage method, with the spinning takingplace through 360°, in stages of 90°. As described above, it is in thisway possible to effect optimum compensation for the offset resultingfrom the Seebeck effect. It is also possible to use Hall plates withjust four terminals, which is of benefit to the sensitivity of the Hallsensor.

Furthermore, according to the method of the invention, to carry outmeasurements on magnetic fields using a Hall sensor, it is advantageousfor the abovementioned determination of a representation of the measuredvariable via electronic processing of the abovementioned four measuredvalues for the detection signal I_(det)(X→Y) only to be allowed to takeplace after this detection signal has been amplified.

In this way, when using the above-described spinning voltage methodthrough 360°, in steps of 90°, it is possible to compensate for both theoffset resulting from the Seebeck effect and the offset of the amplifierin a single step. The said electronic processing of the measured valuesfor the detection signal could, for example, be quadrature demodulation.The method according to the invention for carrying out measurements onmagnetic fields using a Hall sensor may furthermore advantageously becharacterized by the fact that the said electronic processing of thesaid four measured values for the detection signal I_(det)(X →Y)comprises, inter alia, averaging of these measured values.

According to the method of the invention for carrying out measurementson magnetic fields using a Hall sensor, it is preferable to use Hallplates which are formed in n-type silicon semiconductor material.

Hall plates which are formed in p-type silicon have a weaker Hall effectthan n-type plates, with the result that factors causing offset, such asfor example crystal stresses, have in relative terms a greaterdetrimental influence. p-Type Hall plates are therefore less suitablefor achieving optimum offset compensation.

According to the method of the invention for carrying out measurementson magnetic fields using a Hall sensor, it is furthermore advantageous,if the said semiconductor Hall plates are produced in n-type siliconsemiconductor material via a process which has resulted in the substratesurface coinciding with the (100) crystal plane of the siliconsemiconductor material, to use Hall plates whose orientation in thecrystal plane is such that the straight connecting line between theterminals A1 and A2 of the pair of terminals (A1, A2) and the straightconnecting line between the terminals B1 and B2 of the pair of terminals(B1, B2) coincides with or is orthogonal with respect to the [010] or[001] crystal axes or equivalent crystal directions of the siliconsemiconductor material.

When using a Hall plate as described above, with four terminals, andvoltage spinning through 360°, in stages of 90°, it is thereforepossible, according to research carried out by the Applicant, to reducethe offset resulting from mechanical crystal stresses by a factor often. In the case of the abovementioned, known Hall plate with eightterminals and using current spinning, it is never possible to achievethe ideal orientation of the plate, since in that case there will alwaysbe pairs of terminals whose straight connecting line neither coincideswith nor is orthogonal with respect to the [010] or [001] crystal axesor equivalent crystal directions of the silicon semiconductor material.

According to the method of the invention for carrying out measurementson magnetic fields using a Hall sensor, it is advantageously possible touse four of the said Hall plates, each with two pairs of terminals (A1,A2) and (B1, B2), with the second, third and fourth plates respectivelyrotated through 90°, 180° and 270° with respect to the first plate, andthe four plates being parallel-connected as a result of in each case thecorresponding terminals of the four plates being connected to oneanother.

Therefore, in combination with voltage excitation and current detection,it is possible to achieve a reduction in the offset resulting frommechanical crystal stresses and the offset resulting from the Seebeckeffect.

According to the method of the invention for carrying out measurementson magnetic fields using a Hall sensor, it is furthermore advantageousto use a Hall sensor having the said four parallel-connected Hall plateswhich comprises a silicon chip in which the four Hall plates are allintegrated in the same silicon substrate.

This allows optimum compensation for the offset resulting from crystalstresses and the offset resulting from the Seebeck effect. If, moreover,the optimum orientation of the first Hall plate with respect to thecrystal axes has been determined, this is automatically also optimal forthe other three plates, despite their rotated positions.

According to the method of the invention for carrying out measurementson magnetic fields using a Hall sensor, it is preferable to use Hallplates which comprise a layer of n-type silicon located between anunderlying substrate of p-type silicon and a top layer of p-typesilicon.

This structure, which is known as a pinched structure, generates lessflicker noise. Also, pinching results in the formation of broaderdepletion regions in the layer of n-type silicon, and consequently theHall plate effectively becomes thinner, which increases the sensitivityof the plate. One drawback is that a Hall plate with pinching is lesslinear than a plate which is not pinched. The use of voltage excitationand current detection makes it possible to compensate for thenonlinearity which is dependent on an electric voltage.

According to the method of the invention for carrying out measurementson magnetic fields using a Hall sensor, it is advantageously possiblefor the output signal from the abovementioned Hall plate(s) to be passedthrough a delay line with a structure which is such that, after theyhave been summed and averaged, the measured values are delivered withthe same frequency as the frequency with which the said four measurementstages {V_(ex)(X+, Y−), I_(det)(X→Y)} are passed through.

One drawback of spinning methods in general is the fact that a pluralityof sub-measurements have to be carried out for each representation ofthe measured variable. This drawback is compensated for by the use of adelay line as described above. This method is also known as staggeredprocessing. A combination of this with, for example, quadraturedemodulation allows both the offset and the Hall signal to be estimated.The estimates for the offset can then be used to optimize the dynamicrange of the Hall sensor.

The abovementioned object is also achieved, according to the invention,by the provision of an apparatus as described below.

In addition to the evident advantages of the integration of a pluralityof electronic features, another important advantage is the fact that thevariation in, for example, material parameters and temperature betweenseparate integrated circuits, known as inter-chip variation, isgenerally greater than the variation between circuits which areintegrated in the same silicon substrate, known as intra-chip variation.Therefore, the latter variant offers better options for offsetcompensation.

The invention will be explained in more detail in the following text onthe basis of exemplary embodiments of apparatuses according to theinvention, in which the method according to the invention isimplemented, which are diagrammatically depicted in the drawings. Inthis context, it should be noted that the variant embodimentsillustrated are selected purely by way of illustration but do not in anyway restrict the scope of application of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 diagrammatically depicts a variant embodiment of a Hall sensoraccording to the invention in which the method according to theinvention is implemented;

FIGS. 2 to 5 diagrammatically depict currents which occur in Hall platesof the sensor shown in FIG. 1 in various phases of operation of thelatter;

FIG. 6 diagrammatically depicts another variant embodiment of the wiringaround and between the Hall plates shown in FIG. 1 and their terminalswith the wiring;

FIGS. 7 to 10 diagrammatically depict currents which occur in the Hallplates when using the wiring and terminals thereof as shown in FIG. 6;and

FIG. 11 diagrammatically depicts a preferred variant of the wiringaround and between the Hall plates shown in FIG. 1 and their terminalswith the wiring.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description of a Hall sensor with reference to FIG. 1,it is assumed that the Hall plates, electronic features and wiringillustrated are all integrated in the same silicon substrate and formpart of the same silicon chip. Furthermore, it is assumed that use ismade of n-type Hall plates, that the integrated circuit has a pinchedstructure and that the substrate surface coincides with the (100)crystal plane of the silicon semiconductor material used.

The variant embodiment of a Hall sensor according to the inventioncomprises a combined Hall plate composed of four sub-plates 101 to 104.Each sub-plate has a group of two pairs ((A1, A2), (B1, B2)) ofterminals (A1, A2, B1, B2). The terminals of each pair are arranged atopposite corners of the sub-plate, in such a manner that connectinglines between the terminals of the respective pairs are perpendicular toone another. The groups of pairs of terminals of adjacent plates arerotated through 90° with respect to the perpendicular to the plates.

As shown in FIG. 1, the sub-plates 101 to 104 are arranged in a squareformation. The direction in which groups of pairs of terminals ofadjacent plates have been rotated through an angle of 90°, referred tohere as the group orientation, is identical to the direction of theorder in which the sub-plates in question are viewed, referred to belowas the sub-plate orientation.

Corresponding terminals of the four sub-plates are electricallyconnected to one another, so that the four sub-plates are in factconnected in parallel. As can be seen from FIG. 1, for all thesub-plates it is the case that the straight connecting line between theterminals belonging to a pair of terminals is parallel to or orthogonalwith respect to the [010] or [001] crystal axes, which are alsoindicated in the figure.

The four parallel-connected terminals of the combined Hall plate are nowconnected to the four outputs of switching means 106 and 107 and to thetwo inputs of switching means 108 and 109, as shown in FIG. 1. The saidswitching means 106, 107, 108 and 109, which in technical terms can berealized in numerous known ways and using conventional components,receive a clock signal from oscillator 111 and have four switchingstates (1 to 4); in each switching state, an input of the switchingmeans is connected to an output of the same switching means. In thefigure, the arrows in the switching means denote which input isconnected to which output for each switching state. For example, inswitching state 1, the input of switching means 106 is connected to theterminals A1 of the combined Hall plate, and in switching states 1 and2, the terminals B1 of the combined Hall plate are connected byswitching means 108 to the output of the latter switching means.Switching states 1 to 4 are passed through cyclically, as triggered by aclock signal generated by oscillator 111.

The inputs of switching means 106 and 107 are connected to voltagesource 105, which has an impedance that is negligible for use of thesensor, preferably zero, and delivers a voltage which is suitable foruse as excitation voltage for the Hall plates. The switching means 106and 107 and the parallel connection of the sub-plates 101, 102, 103 and104 of the combined Hall plates now ensure that, for each cycle of fourswitching states, the said excitation voltage from voltage source 105 isapplied twice to each of the two pairs of terminals of the sub-plates,once with an inverted sign. Each time per switching state that theexcitation voltage is applied to four parallel-connected pairs ofterminals of the four sub-plates, the switching means 108 and 109 ensurethat the total of the (Hall) currents which pass through the other fourparallel-connected pairs of terminals of each sub-plate are read(detected) and fed to two differential inputs of an amplification means110. The latter may, for example, be a current amplifier. The impedanceof the amplifier means 110 between the differential inputs is negligibleand preferably zero. Each of the differential inputs of the amplifiermeans 110 has a high, preferably infinite impedance to earth (ground).This way, the currents which then pass through the Hall plates and thedifferential inputs of the amplifier means 110 are approximatelyshort-circuit currents and form a representation of the magnetic fieldstrength measured by the Hall sensor. Following the amplification means110, the sign of two of the four measured values which are suppliedduring a cycle of four switching states is inverted by the two switchingmeans 112 and 113. These switching means, which in technical terms canbe realized in a wide range of known ways and using conventionalcomponents, receive a clock signal from oscillator 111 and, like theswitching means 106 to 108, have four switching states (1 to 4), asindicated in the figure.

The variant embodiment of the apparatus according to the inventiondescribed here is in fact a spinning voltage Hall sensor with fourterminals. The currents which are read can be processed further in bothanalogue and digital form, depending on the requirements of the specificapplication. Analogue-digital converters and other auxiliary electronicmeans are of no relevance to the present description and are thereforenot depicted in the figure.

On account of the fact that the “spinning” comprises four stages,coinciding with the four abovementioned switching states, the Hallsensor described here could supply an output value after each cycle offour stages. To obtain a representative measured value more quickly, itis possible to use staggered processing. In this case, the outputs ofthe switching means 112 and 113 are connected to a delay line comprisingthree sections 114, 115 and 116. Under the control of the oscillator111, during each switching state an output signal from the switchingdevices 112 and 113 is fed to the delay line. The outputs of the saidswitching devices 112 and 113 and the outputs of each of the threesections 114, 115 and 116 of the delay line are connected to an addingmeans 117, which under the control of oscillator 111 adds up the outputsignals of the switching features 112 and 113, and the output signalsfrom the sections 114, 115 and 116 of the delay line, during eachswitching state. The adding means 117 supplies, at an output 118 of theHall sensor, an output signal which represents an average measured valueof which the average moves with the frequency of the oscillator 111.

FIGS. 2 to 5 show, without reference numerals and letters for the sakeof clarity, the four Hall plates 101 to 104 from FIG. 1 for therespective four switching states described. In FIGS. 2-5, arrows showthe currents which pass through the plates 101-104 and, at the sametime, through the voltage source 105 during the four abovementionedswitching states of the switching means 106 and 107.

It can be seen from FIGS. 3 and 5 that the currents shown togethercorrespond to a current through a loop comprising a coil with a singleturn. Since the plates 101-104 are of limited size, the integral of themagnetic flux in the plane of the loop will not be equal to zeroirrespective of the direction of the current. As a result, in thesituations shown in FIGS. 3 and 5, this current generates a residualmagnetic field which has an adverse effect on the measurement of anexternal magnetic field.

FIG. 6 shows the Hall plates 101-104, with the terminals A1, A2, B1, B2arranged in such a manner, and with associated wiring which is such,that the group orientation of the terminals A1, A2, B1, B2 is oppositeto the sub-plate orientation. As a result, the terminals of thesub-plates in the center of the combined plate are alternately connectedto two different terminals of the switching means 106 and 107 for thesame pair of terminals (A1, A2 in FIG. 6).

FIGS. 7 to 10, like FIGS. 2 to 5, use arrows to show the direction ofthe currents which pass through the plates 101-104 and, at the sametime, through the voltage source 105 in the four switching states of theswitching means 106 and 107.

The situations shown in FIGS. 7 and 9 correspond to the situations shownin FIGS. 2 and 4.

The situations shown in FIGS. 8 and 10 appear to correspond to thesituations shown in FIGS. 3 and 5. However, in the situations shown inFIGS. 8 and 10, the integral of the magnetic flux generated by thecurrents over the finite surface area of the Hall plates is minimal(zero under ideal conditions and without external magnetic field). As aresult, these currents will generate (virtually) no residual magneticfield in the sub-plates, and consequently they have no adverse effect onthe measurement of an external magnetic field. For this reason, thearrangement of the sub-plates shown in FIG. 6 is preferred.

The currents in the various sections of the wiring between and aroundthe sub-plates 101-104 also appear to have the ability to cause aresidual magnetic field in the sub-plates, which has an adverse effecton the measurement of an external magnetic field, as a function of thearrangement of the wiring. FIG. 11 shows an arrangement of the wiringwhich generates a minimal residual magnetic field. Therefore, thearrangement of the wiring shown in FIG. 11 is preferred. The same alsoapplies to other arrangements of the wiring to obtain a similar result.

It should be noted that it will be clear to a person skilled in the art,on reading the description and the claims, that various alternativeembodiments are possible within the scope of the appended claims. Forexample, it is possible for the plurality of Hall plates to be arrangedin different locations and with different orientations with respect toone another from those described here and shown in the figures. Withinthe scope of the claims, it is possible for a Hall plate to be arrangedeven with its main plane perpendicular to a main plane of a substrate,and for its terminals to be arranged at a main plane of the substratealong a single edge of the Hall plate, in which case terminals belongingto one pair of terminals alternate with terminals belonging to the otherpair of terminals.

1. Method for measuring an entity of a magnetic field using a Hallsensor, which is provided with at least one Hall plate which includes agroup of two pairs ((A1, A2), (B1, B2)) of terminals (A1, A2, D1, B2)located at a distance from one another, an excitation signal beingsupplied from a source to one pair of terminals, and a detection signal,which forms a representation of the entity, being tapped off from theother pair of terminals by a processing circuit, wherein the source is avoltage source of which an impedance is negligible for use of thesensor, and the processing circuit has a negligible input impedance fortapping off the detection signal as a short-circuit current.
 2. Methodaccording to claim 1, wherein the measurement of the entity is carriedout in cycles of in each case four sub-measurements, to provide fourmeasured values for the entity, with the pairs of terminals of theplates being alternately connected to the voltage source and to theprocessing circuit, the polarity of the voltage source being reversedduring two sub-measurements with respect to the other twosub-measurements.
 3. Method according to claim 1, wherein themeasurement of the entity is carried out in cycles of in each case foursub-measurements, to provide four measured values for the entity, withthe pairs of terminals of the plates being alternately connected to thevoltage source and to the processing circuit, the polarity of thevoltage source being reversed during two sub-measurements with respectto the other two sub-measurements, the processing circuit amplifies thedetection signal prior to processing of the detection signal.
 4. Methodaccording to claim 1, wherein the measurement of the entity is carriedout in cycles of in each case four sub-measurements, to provide fourmeasured values for the entity, with the-pairs of terminals of theplates being alternately connected to the voltage source and to theprocessing circuit, the polarity of the voltage source being reversedduring two sub-measurements with respect to the other twosub-measurements, the processing of the four measured values comprisesthe reversing of the polarity of the measured values of the twosub-measurements for which the polarity of the voltage source wasreversed with respect to the other two sub-measurements, and themeasured values of the two other sub-measurements and the two measuredvalues with reversed polarity are summed.
 5. Method according to ofclaim 1, wherein the measurement of the entity is carried out in cyclesof in each case four sub-measurements, to provide four measured valuesfor the entity, with the pairs of terminals of the plates beingalternately connected to the voltage source and to the processingcircuit, the polarity of the voltage source being reversed during twosub-measurements with respect to the other two sub-measurements, Hallplates which are made from n-type silicon semiconductor material areused.
 6. Method according to claim 5, wherein if the said semiconductorHall plates are made from n-type silicon semiconductor material using aprocess which resulted in the substrate surface coinciding with thecrystal plane of the silicon semiconductor material, plates are usedwhose orientation in the crystal plane is such that a straightconnecting line between the terminals of each pair of terminalscoincides with or is orthogonal with respect to the [010 ]or [001]crystal axes or equivalent crystal directions of the siliconsemiconductor material.
 7. Method according to of claim 1, wherein themeasurement of the entity is carried out in cycles of in each case foursub-measurements, to provide four measured values for the entity, withthe pairs of terminals of the plates being alternately connected to thevoltage source and to the processing circuit, the polarity of thevoltage source being reversed during two sub-measurements with respectto the other two sub-measurements, four Hall plates are integrated in acommon silicon substrate in such a maimer that the group of terminals ofeach Hall plate, with respect to a perpendicular to a main plane of theplates, is rotated through 90, 180 and 270°, respectively, with respectto the other groups of terminals, and the same terminals of thedifferent groups are connected to one another in accordance with thedifferent orientation for adjacent plates.
 8. Method according to claim7, wherein the Hall plates are arranged in a square formation, with anorientation of their groups of terminals which is such that a directionin which one looks from one Hall plate towards an adjacent Hall plate isopposite to a direction in which the group of terminals of the one Hallplate is rotated through 90° with respect to the group of terminals ofthe other Hall plate.
 9. Method according to of claim 7, wherein wiringto, from and between the Hall plates is arranged in such a manner thatcurrents running from and to the voltage source generate magnetic fieldswhich substantially cancel one another out in the main plane of the Hallplates.
 10. Method according to claim 1, wherein Hall plates whichcomprise a layer of n-type silicon located between an underlyingsubstrate of p-type silicon and a top layer of p-type silicon are used.11. Method according to claim 1, wherein the measurement of the entityis carried out in cycles of in each case four sub-measurements, toprovide four measured value for the entity, with the pairs of terminalsof the plates being alternately connected to the voltage source and tothe processing circuit, the polarity of the voltage source beingreversed during two sub-measurements with respect to the other twosub-measurements, the processing circuit stores the measured values forevery four successive sub-measurements, and for each sub-measurement thefour measured values obtained last are summed to give a processedmeasured value for the variable.
 12. Method according to claim 1,wherein switching means are arranged to alternately connect the pairs ofterminals of the source and the processing circuit between the pairs ofterminals and the source and the processing circuit.
 13. Apparatus formeasuring an entity of a magnetic field using a Hall sensor, which isprovided with at least one Hall plate which has a group of two pairs((A1, A2), (B1, B2)) of terminals (A1, A2, B1, B2) located at a distancefrom one another, one pair of terminals being connected to a source forsupplying an excitation signal to the one pair of terminals, and anotherpair of terminals being connected to a processing circuit for tappingoff and processing a detection signal from the other pair of terminals,wherein the source is a voltage source of which an impedance isnegligible for use of the sensor, the processing circuit has anegligible input impedance for tapping off the detection signal as ashort-circuit current.
 14. Apparatus according to claim 13, whereinswitching means are arranged to alternately connect the pairs ofterminals of the source and the processing circuit between the pairs ofterminals and the source and the processing circuit.
 15. Apparatusaccording to claim 13, wherein four Hall plates are provided in a squareformation and integrated in a single substrate, the groups of terminalsof the Hall plates being oriented in such a manner with respect to aperpendicular to a main plane of the plates that one group of terminalsof a Hall plate is rotated through 900 with respect to a group ofterminals of an adjacent Hall plate, in a direction which is opposite tothe direction in which the other Hall plate follows the one Hall plate,and the same terminals are connected to one another in accordance withthe different orientation for adjacent plates.
 16. Apparatus accordingto claim 13, wherein a wiring is connected to the terminals of the Hallplates, the wiring having an arrangement which is such that currentsrunning from and to the voltage source generate magnetic fields whichsubstantially cancel one another out in the main plane of the Hallplates.